In recent years, introduction of information-oriented execution is progressing into construction work in which a work machine is used. The information-oriented execution means execution in which information and communication technology (ICT) and RTK-GNSS (Real Time Kinematic-Global Navigation Satellite) are fully used when execution works such as construction works is performed using a work machine such as a hydraulic excavator. Specifically, in the information-oriented execution, a position of a work point of a work implement in the work machine is detected, and the work implement is automatically controlled based on the detected work point, thereby efficiently performing the execution work to obtain a high-accuracy execution result.
For example, in the case that the work machine is the hydraulic excavator, the work point of the work implement in the information-oriented execution is a position of a cutting edge of a bucket. The position of the cutting edge is computed as a position coordinate on design based on parameters such as a positional relationship between a GNSS antenna and a boom foot pin, lengths of a boom, a dipper stick, and the bucket, and stroke lengths of a boom cylinder, a dipper stick cylinder, and a bucket cylinder.
Dimensions of a design value are used as the lengths of the boom, the dipper stick, the bucket, and each cylinder, which are used in the above computation. However, the actual dimensions include an error due to manufacturing tolerances and assembly tolerances with respect to the design value. Consequently, the position coordinate of the cutting edge computed from the design value is not always matched with the position coordinate of the actual cutting edge, which results in a decrease in accuracy of position detection of the cutting edge. In order to improve the accuracy of the position detection of the cutting edge, it is necessary to calibrate the parameter in the design value used for the computation based on the position coordinate obtained by the actual position measurement, and it is necessary to perform calibration work such as the position measurement.
For example, International Publication No. 2015/040726 (PTD 1) discloses a technique of attaching a prism mirror that reflects projection light from a total station to the cutting edge of the bucket and of measuring the light reflected from the prism mirror to measure the position of the cutting edge.